In addition to Stevens, who is the sole Protestant on the bench, there are currently six Catholics and two Jews -- Justices Ruth Bader Ginsburg and Stephen Breyer -- on the bench. Kagan, who is Jewish, would be the third.

At least one Protestant justice has served at all times since the Supreme Court was established in 1789. But the importance of religion when it comes to choosing and confirming Supreme Court justices has declined considerably over time, scholars say. There are other factors that have since come to the forefront, such as gender and race.

"Religion used to be the most important consideration for the court. There was a Catholic seat, there was a Jewish seat," said Jeffrey Rosen, a professor of law at George Washington University and author of "The Supreme Court." "Recently, it hasn't mattered at all.

At a time when a majority of Americans call themselves Protestant, "it's a fascinating truth that we've allowed religion to drop out of consideration on the Supreme Court, and right now, we have a Supreme Court that religiously at least, by no means looks like America," Rosen said.

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Elena Kagan Praises Justice John Paul Stevens

A Gallup poll released earlier this month found that a majority of Americans did not care whether President Obama picked a Protestant to fill Stevens' seat. Only 7 percent of those polled said it was essential that he pick a Protestant, while 66 percent said it did not matter.

The lack of importance given to the justice's faith signals a dramatic shift in the way Americans think about religion.

"As long as there's something of a mix, as long as no one religion occupies every seat on the court, it's not an issue that most voters in this day and age find to be very salient," said Guy-Uriel Charles, a professor of law at Duke University.

Historically, the U.S. Supreme Court was composed mostly of white, male Protestants, but over time, religion became a more defining factor, with special attention paid to appointing non-Protestant justices. The first Catholic justice, Roger Taney, was appointed in 1836, and the first Jewish justice, Louis Brandeis, in 1916.

For much of the 20th century, the court had, as Rosen pointed out, a Catholic seat and a Jewish seat. However, U.S. presidents didn't always pay attention to that. In 1969, following the resignation of Justice Abe Fortas, President Nixon filled what was considered the Jewish seat with a Methodist, Harry A. Blackmun.

In 1949, President Truman appointed Justice Sherman Minton to the Catholic seat. Minton's wife was Catholic but, at the time, he identified as a Protestant.

Religion and Supreme Court Justices

The White House said President Obama did not apply a "religious litmus test" when picking his nominee.

"He was looking for the person who combined the best qualities, that could be the best justice at this time, and it turned out to be Elena Kagan and the fact that her faith was not -- was not an issue," senior adviser David Axelrod said in an interview with ABC News' Jake Tapper.

Supreme Court justices often tend to distance their religious affiliations from their work. After all, the justices are often faced with hot-button issues that involve religious issues, such as abortion and prayer in schools.

Speaking at Georgetown University in April, Justice Ruth Bader Ginsburg argued that despite the lack of diversity on the bench, Obama should not consider religion when he makes his pick.

"We're not representative of the United States as far as religion is concerned. We have on the court six Catholics, two Jews and only one white Anglo-Saxon Protestant. That's unusual in U.S. society," she said. "But I don't think that any of us would like to be identified as -- say for me -- the Jewish justice or the Catholic justice. We happen to have a certain religious heritage, but we should not be chosen for the court ... on that basis."

But while some justices have purposefully distanced themselves from their faiths, others have spoken openly about the importance of religion and how it has affected their lives.

"For Supreme Court justices, like for many people, religious identity is a central part of who they are," Rosen said. "Justice Breyer says he was very much influenced by his experience, growing up Jewish. Justice [Antonin] Scalia and Justice [Clarence] Thomas, who attend church regularly, take positions in their opinions that correspond very closely to that of their faith."

"We've forgotten that religions can be an important part of the identity as well," he said.

In an interview with The Associated Press, former Justice Sandra Day O'Connor spoke in favor of why the president should look at religion when picking out Justice Stevens' replacement.

"I think that religion should not be the basis for an appointment, [but] one would expect somewhere in the nine to see a Protestant or two," she said.

For now, however, Kagan's nomination and the possibility of no Protestants on the high court are not likely to cause any tussle, experts said. The issue of justices' religious affiliations will likely recede into the background unless there is a major case that changes Americans' minds.

"If the court takes on a number of cases and decides them in a way that's incompatible with the preference of the majority, perhaps religion might be salient once again," Charles of Duke University said, but "people are increasingly less concerned with the religious diversity."

ABC News' Dennis Powell and Ariane de Vogue contributed to this report.